Radiation Protection Flashcards
Background radiation dose to a member of public??
2.5mSv
What is Air Kerma?
Total Kinetic energy released per unit mass by an ionising radiation
Units Gy
Measurement in air used as air has a similar atomic number to soft tissue (7) and effect on radiation on changes in temp are so small that they can be ignored.
At lower dose: AIR KERMA = ABSORBED DOSE
At higher doses: AIR KERMA > ABSORBED DOSE
Absorbed dose?
Amount of deposited energy in a substance
Units of Gy
Relationship between:
Absorbed dose
Equivilent dose
Effective dose
Absorbed dose in Gy
multiply by Radiation weighting factor
Equivilent dose in Sv
multiply by tissue weighting factor (had no units)
Effective dose in Sv
(absorbed dose weighted for ratiosensitvity of tissue)
What is Radiation weighting factor?
Takes into account effects of different types of radiation
Alpha particles highest: 20
Protons: 2
X-ray, beta, gamma, positrons: 1
Does effective dose relate to stochastic or deterministic effect?
Risk of stochastic effects in linked to the EFFECTIVE DOSE
What are the tissue weighting factors?
A value given to the different organ sensitivies to radiation
Bone, colon, lung, breast: 0.12
Gonads: 0.08
Skin and brain: 0.01
When is the highest risk to the fetus?
All or nothing effect during early fetal stage (0 - 2 weeks)
First trimester is very sensitive: high incidence of congenital malformations
Childhood cancer biggest risk in FIRST TRIMESTER
What is threshold dose for CNS malformations to fetus?
100 - 200mGy
When to suspend breastfeeding?
Completly if: had course of I131
3 weeks if:
- I131, I125
- Gallium
- Sodium
- Thallium
12 hours after:
- Iodine 131 hippurate
- All Technetium 99m compounts (except Tc red cells which is 4 hours)
4 hours:
- Technetium 99m red cells
- DTPA
- Phosphonates
Effective Dose limits for employee >18years
(Effective Dose governs STOCHASTIC effect risk)
20mSv per year
or
100mSv in any consecutive 5 years (with a max of 50mSv per any single year)
Effective dose limits for trainee <18 years
6mSv
Effective dose limit for <16 year (trainee or anyone)
1mSv per year
Dose to abdomen for person of reproductive capacity (STAFF)
13mSv in any consecutive 3 months
What is DAP?
DAP = entrance skin dose x cross sectional area of x-ray beam
- A measure of patient exposure
- Not affected by distance
Units Gy/cm2
The DAP meter must intercept the ENTIRE area of the x-ray beam
Equivilent dose limits?
Deterministic
Lens: 20mSv over 18 years
15mSv under 18 years and indirectly from another person
Extremeties and Skin: 500mSv over 18 years
150mSv for under 18 years
50mSv for thosse exposed indirectly after exposure of another person
What is controlled area?
4 points
Where person working their may be subject to:
- Effective dose >6mSv
- Lens dose 15mSv
- Equivilent dose of 3/10 of any relevant dose limit
- External dose rates 7.5microSv/hour averaged over the day
What is supervised area?
If anyone in the area is likely to receive a dose of 1mSv/year or 1/10th or any dose limit
When to notify HSE?
- Doses exceed staff dose limits
- Exposures much greater than intended
- Loss or theft or source
- Release of spillage leading to significant contamination
What is yearly background radiation dose?
2.7mSv approx
Radiation dose - flights etc
- Transatlantic flight: 0.08mSv
- Nucleur power station worker: 0.18mSv
- Annual average radon dose: 1.3mSv (out of total 2.7mSv average) - over 50% of dose
- Average annual radon dose in Cornwall: 6.9mSv
Radon gas emits alpha particles
Medical contribution = 14% to yearly dose
- CT contributes 47% of medical dose and is only 4% of exams
Nucleur Fallout (from testing of Nucleur weapons years ago)
- dose is so minimum, just 0.2%
What causes direct damage to tissues?
Rupture of Covalent bonds
What causes indirect damage to tissues?
Production of free radicals
Free radicals cause chemical changes in tissues
Are absorbed doses higher or lower than effective dose?
Absorbed doses tend to be higher
What is the average radiation dose per hour of flying?
4µSv/hour
What do tissue weighting factors give an indication of?
An estimate of the MORTALITY from cancers per mSv to that organ or tissue
Do not account for likelihood of getting cancer
Does Skin and Bone surface have same tissue weighting factor?
Yes
0.01
Deterministic dose effects
Lowest is fetal abnormality is 0.1 - 0.5Gy
Most things is 2 - 5Gy
Cataracts is 5Gy
Fatal whole body dose is 5Gy
Deterministic effect gets more severe as dose increases
What is equivilent dose limit for the abdomen of a female employee of reproductive age?
13mSv in 3 months
Who has overall responsibility for radiation protection?
Employer
What is justification?
Justification to carry out or decline an examination if:
- benefit of doing exam outweighs risk (carry out exam)
- benefit of doing exam does not outweigh risk (decline to do exam)
Governing body of IRR?
HSE (Health and safety excecutive)
Gornerning body of IRMER for reporting overexposures to patients?
CQE (Care quality commission)
Barium doses
Barium meal - 3mSv
Barium enema - 7mSv
Does absorbed dose depend on organ mass?
NO
Time of greatest risk of foetal abnormalities?
First trimerster
3 - 8 weeks
Mental retardation?
First and second trimester
8 - 15th week
Childhood cancer risk?
Maximal in first trimester
Risk of fatal cancer from exposure?
1 in 20,000 per mSv
Or 5% per sievert
Risk of childhood cancer from exposure in utero?
1 in 33,000 per mGy
3% per gray
What does radon produce?
Alpha particles
What can DAP ionisation chamber be used for?
- x-ray
- fluoro
NOT CT
TLDs
Have:
- linear response over wide dose range
- generally used with filters
- can be reused. can only be read out once
- can detect shallow and deep doses
- Have similar sensitivity to film dose badges
- can measure finger and eye doses
- Precision of 15% for low doses
- Precision of 3% for high doses
Need heated to 300 degrees for read out
Need to be annealed after read out
TLD holder helps differentiate between skin and deeper doses
Disadvantages:
- cannot measure dose rate
- cannot differentiate between radiation types
- affected by heat
Film Badges
Advantages:
- can identify type of exposure
- Highly energy depdendent due to the different atomic numbers of Silver and Bromide
- sensitivity is 0.1mSv
- use double sided film emulsion (without a screen)
- similar sensitivity to TLDs
- provide a permanent record
- can detect beta radiation and radioactive splash
No intensifier on a film badge
Disadvantages:
- prone to fogging
- must be developed and read out
- require calibration
OSL Badges
Optically stimulated luminescence
Use aluminium oxide
Intensity of luminescence is proportional to the absorbed dose
Can read dose as low as 0.01mSv
Electronic dosimeters
- Accurate to 1µSv
- Require a filter
- 100 times more sensitive than TLDs
- Provide a direct reading
- can be used to detect radioactive contamination
ARE HIGHLY ENERGY DEPENDENT
- Geiger muller counters are counted as electronic dosimeters too
Can secondary electrons cause ionization?
Yes
Are writing protocols for doses and having medical physics expert part of IRMER or IRR?
Part of IRMER
Radiation protection supervisor duties?
- Investigation of excessive doses
- ensuring staff follow local rules
- ensuring QA processes in place
- risk assessment for pregnant staff
Can DAP be converted into effective dose?
Yes
- Can be converted into EFFECTIVE DOSE using conversion factor
- Conversion factors depend on the region of the body
DRLs
Are they set locally?
- Are set for standard sized patients (not taken into account for overweight folk)
- Yes they are set locally by employer but they must be close to the nationally set DRLs
DRLs are set using ESD, screening times and DAP as references
Wall protection requirements?
Lead - 2mm
Concrete - 1.5cm
Barium plaster - 2cm
Brick - 2.4cm
(equals 2mm of lead)
Pregnant worker
Should inform EMPLOYER
Should not need to alter her working practice
Pointers
- Leakage of radiation should be less than 1mGy per hour at distance of 1m
- Operator should stand 2m from x ray tube
- Filtration in dentistry is 1.5mm aluminium
- Lead apron 45 x 40cm long
Does risk of stochastic effects increase LINEARLY or exponentially with dose?
Increases Linearly
Known as the Linear no threshold theory
Increased risk with lower age (kids more likely to get a cancer than an adult)
For stochastic effects:
- Risk of leukaemia is usually peaking at around 7 years
- Risk of solid organ tumour is around 40 years
Who are overexposures due to equipment fault reported to?
Has to reported under IRR if it is due to equipment
Reported to HSE
IRR
- Employer must state their intention to HSE about using ionising equipment for FIRST time (not for equipement change)
- Employers responsibilty to perform a risk assessment before installing new equipment (not manufacturers responsibility)
Yearly effective dose limit for:
Adults/Under 18/Carer comforter
Adult >18: 20mSv
Under 18: 6mSv
Member of public or under 16: 1mSv
Carer of comforter: 5mSv in any period over 5 years
Who governs testing of equipment?
IRMER and IRR
What is a dose constraint?
It is the maximum dose than can be exceeded
Dose to adults per year. Can it exceed 20mSv/year?
Yes it can as long as it doesnt exceed:
50mSv in a single year
100mSv over 5 years
What can DRLs be expressed as?
- Screening time
- mA
- kV
- DAP
How much radiation does lead apron transmit? 0.35mm
0.35mm transmits 3%
0.25mm transmits 5%
What are the remainder organs in tissue weighting factors?
- Kidneys
- Adrenal
- Gallbladder
- Heart
- Lymph nodes
- Muscles
- Pancreas
- Uterus
- Prostate
- Small bowel
- Thymus
All 0.01 each
Changes new in IRR17
Lead Aprons
Radiation Doses for different exams
Radiation protection advisor and medical physics expert
IRMER or IRR
Medical physics expert - IRMER
RPA - IRR
RPS and RPA
Is equivilent dose used to set occupational dose organ limits?
Yes
